Field
The present disclosure relates to a sheet conveying device.
Description of the Related Art
Image forming apparatuses, such as a copying machine, a printer, and a facsimile, have been required to have smaller size and higher speed of duplex printing on sheets.
In a typical method for performing printing (image formation) on both surfaces of a sheet, after one surface of the sheet is printed, the sheet is conveyed to a duplex conveying path by rotating rollers nipping the sheet backward. By conveying the sheet to a transfer part and a fixing part in an inverted state, the other unprinted surface is printed. At this time, the rollers rotating backward are provided in two ways, that is, they are provided on a discharging path for single sheet surface feeding, or on a conveying path used only during duplex printing. In the former case, however, until the rollers rotate backward and the sheet comes out of the nip, the next sheet cannot be conveyed. This is disadvantageous for speedup. Further, in the latter case, two pairs of rollers are necessary, and this disadvantageous for size reduction.
Accordingly, in an image forming apparatus described in Japanese Patent Laid-Open No. 2000-26002, two driven rollers are opposed to one discharge roller (so-called triple roller structure) to form two nips. This achieves both speedup and size reduction.
However, in the structure described in Japanese Patent Laid-Open No. 2000-26002, the rotation centers of the triple rollers (driving roller and two driven rollers) are disposed on one straight line. Hence, when the driving roller rotates forward and backward, the direction of force changes, and the driving roller and the driven rollers sometimes shake in the sheet conveying direction and the up-down direction. When the rollers shake, conveyance of the sheet becomes unstable. This may cause a jam in some cases.